[0001] The present invention relates to a method for controlling a diesel engine with a
common-rail injection system during regeneration of the particulate filter.
[0002] As is known, in order to reduce atmospheric pollution, the regulations in most countries
are imposing increasingly stringent limits on the composition of the exhaust gases
produced by internal combustion engines.
[0003] In particular, with regard to diesel engines, the main problems consist in the presence,
within the exhaust gases, of nitrogen oxides (NOx) and particulate, while carbon oxides
(CO) and hydrocarbons (HC) do not pose a particular problem.
[0004] Many methods have been proposed hitherto in order to reduce to minimum values the
quantity of particulate present within the exhaust gases introduced into the atmosphere.
Of these, however, without doubt the arrangement, along the gas exhaust pipe, of a
particulate filter (DPF - Diesel Particulate Filter), also known as "soot catcher"
or "soot trap", has been recognised for many years in the motor car industry as the
definitive solution to the problem of particulate emissions from diesel engines.
[0005] In more detail, a particulate filter generally consists of parallel channels with
porous walls which are alternately obstructed. The obstructions force the exhaust
gases to pass through the side walls of the channels such that the non-combusted particles
forming the particulate are firstly retained inside the porosity of the said side
walls and then, when the latter are completely filled, accumulate on the internal
surfaces of the channel walls, forming a porous layer.
[0006] With the increase in the accumulation of particulate on the internal surfaces of
the channel walls, the reduction in pressure on the particulate filter and therefore
the backpressure produced by the said particulate filter also increase.
[0007] The particulate therefore cannot be accumulated indefinitely since large accumulations
cause:
- a deterioration in performance, drivability and consumption of the engine, until,
in the most extreme case, stalling of the engine occurs; and
- destruction of the said particulate filter in the case of self-ignition and uncontrolled
combustion of the particulate; in fact, the presence of large quantities of particulate,
in particular driving conditions, may trigger "critical" regeneration phenomena consisting
in the sudden and uncontrolled combustion of particulate: consequently, the high temperatures
generated inside the ceramic lattice of the particulate filter may result in damage
to the filter itself.
[0008] It is therefore necessary to remove periodically the particulate which has accumulated,
performing so-called "regeneration" of the particulate filter. In particular, in the
motor car industry, "regeneration" of the particulate filter is understood as meaning
combustion of the accumulated particulate (composed mainly of carbon, C) which, in
contact with the oxygen present in the exhaust gases, is converted into carbon monoxide,
CO and carbon dioxide, CO
2.
[0009] However, this reaction occurs naturally (i.e. without the use of additives) only
at temperatures higher than about 600°C and these temperature levels are much higher
than those which are measured at the inlet of the particulate filter during normal
operating conditions of the engine.
[0010] It is therefore necessary, in certain conditions, i.e. when given levels of accumulated
particulate are detected within the particulate filter, to raise artificially the
temperature of the exhaust gases at the inlet of the said particulate filter so as
to trigger automatically combustion of the particulate.
[0011] The regeneration of a particulate filter forms the main problem associated with the
use of this type of filter in the motor car industry.
[0012] Numerous methods have been proposed and/or used hitherto in order to raise artificially
the temperatures of the exhaust gases at the inlet of the particulate filter and trigger
combustion of the particulate.
[0013] In particular, the methods of automatically triggering combustion of the particulate
may be roughly divided into two main categories, depending on the type of approach
used: the first category involves automatic triggering methods which are based on
the use of an additive in the diesel fuel which, acting as a catalyst, allows a reduction
in the temperature at which regeneration starts by about 100-150°C, while the second
category involves those methods of automatically triggering combustion of the particulate
which are based on control of combustion of the engine.
[0014] In particular, the methods of automatically triggering combustion of the particulate
based on the use of an additive require:
- an exhaust system comprising a catalyst and a particulate filter which are incorporated
inside a single housing (canister);
- a particulate filter with a very large volume, typically equivalent to about twice
the cubic capacity of the engine;
- a gas fuel additive (based on cerium) which allows a reduction in the temperature
for automatic triggering of regeneration by about 100-150°C;
- a very complex system for adding and automatically metering the additive on-board
the vehicle; and
- engine control methods for increasing the temperature at the inlet of the particulate
filter, since the necessary temperature levels cannot in any case be reached in conditions
of normal use of the engine; in fact, this type of system functions correctly only
in the case of operation of the engine under medium loads, while in the case of prolonged
operation under low loads (for example when driving in towns) and/or in the presence
of low external temperatures (in winter), the temperature of the exhaust gases in
many cases does not manage to reach the self-triggering temperature.
[0015] The methods of automatically triggering combustion of the particulate based on the
use of an additive, although they allow automatic triggering of regeneration of the
particulate filter in the region of 450-500°C and the particulate filter produces
a low backpressure, have the following major limitations which prevent adequate and
complete exploitation of all their positive aspects:
- complexity, in particular of the system for adding and automatically metering the
additive;
- need for installation of a large-volume particulate filter since the additive present
in the diesel fuel leaves a deposit of ash inside the particulate filter which gradually
increases;
- need to "clean" in any case the particulate filter of the ash about every 80,000 km,
despite the large volume of the particulate filter; cerium, in fact, produces a large
quantity of ash which accumulates inside the filter together with the particulate
and cannot be eliminated by means of regeneration; this therefore results in a gradual
increase in the backpressure of the filter on the engine with the increase in distance
travelled by the vehicle and the consequent need to perform periodically disassembly
and cleaning of the filter in order to eliminate the ash which has accumulated; and
- high cost, both in the case of the system for adding and automatically metering the
additive and in the case of the large-volume particulate filter.
[0016] Owing to the numerous disadvantages listed above, for some time now nearly all motor
car manufacturers have preferred the methods of automatically triggering combustion
of the particulate not based on the use of an additive to those based on the use of
an additive.
[0017] One of the solutions proposed and used in the past in order to raise artificially
the temperature of the exhaust gases in the particulate filter without the use of
an additive envisaged equipping the said particulate filters with heating elements
which were periodically activated in order to raise the temperature of the particulate
filter to that for automatic triggering of combustion of the trapped particulate.
[0018] More recently, instead, solutions have been proposed where the increase in the temperature
of the exhaust gases at the inlet of the particulate filter is obtained by means of
methods involving control of the engine combustion.
[0019] In particular, the methods commonly used in order to raise the temperature at the
particulate filter inlet are:
- regulating the main injection in order to obtain retarded combustion;
- performing a post-injection following the main injection; or
- modulating the intake air so as to reduce it (for example reducing the supercharging
or throttling the intake).
[0020] In detail, the method based on delay of the main injection has drawbacks due to the
fact that the main injection may not be retarded beyond a certain limit, otherwise
it would cause an unstable combustion which would result in misfiring, with the consequent
production of white/blue smoke and problems associated with driving performance, in
particular lack of response. For these reasons, with this method it is not possible
to obtain, at low speeds and with low engine loads, high temperatures at the particulate
filter inlet.
[0021] International patent application
PCT/IT95/00124 filed on 21.7.95 by the Applicant and published on 8.2.96 under number
WO-A-96 03571 instead proposes a method in which the increase in the temperature of the exhaust
gases at the particulate filter inlet is obtained by performing, in addition to the
main injection, a post-injection during the expansion step.
[0022] In particular, the timing of post-injection with respect to the main injection and
the quantity of injected fuel are determined so that combustion of the fuel during
the expansion phase is such as to produce an increase in the temperature of the exhaust
gases sufficient to automatically trigger regeneration of the particulate filter.
[0023] International patent application
PCT/IT95/00123 filed on 21.7.95 by the Applicant and published on 8.2.96 under number
WO-A-96 03572 also proposes a method where the increase in the temperature of the exhaust gases
at the particulate filter inlet is obtained by performing, in addition to the main
injection, a post-injection during the exhaust phase.
[0024] In particular, since generally the particulate filter is incorporated inside a single
housing (canister) together with a DeNOx catalyst arranged upstream of the particulate
filter, a post-injection performed mainly during the engine exhaust phase has the
effect that the injected fuel does not contribute, albeit to a small degree, to combustion
and therefore reaches the catalyst directly in non-combusted form.
[0025] The non-combusted hydrocarbons thus introduced into the catalyzer trigger an exothermic
oxidation reaction which produces raising of the temperature of the exhaust gases
at the catalyzer outlet and consequently an increase in the temperature of the exhaust
gases entering the particulate filter.
[0026] Compared to the methods of automatically triggering combustion of the particulate
based on the use of an additive, the methods of automatically triggering combustion
of the particulate based on control of combustion of fuel require:
- a particulate filter having a volume substantially equal to the cubic capacity of
the engine, i.e. half that required by the methods of automatically triggering combustion
of the particulate based on the use of an additive:
- an exhaust system which may alternately:
- have a configuration similar to that required by the methods of automatically triggering
combustion of the particulate based on the use of an additive, namely comprising a
catalyst and a particular filter which are incorporated inside a single housing (canister);
or
- comprise a single filter with deposited thereon both the oxidizing elements of the
catalyst and metals (Ce + Pt) which reduce the self-ignition temperature (catalysed
soot filter);
- no additive in the diesel fuel;
- no system for adding and automatically metering the additive on-board the vehicle;
and
- engine control methods for increasing the temperature at the particulate filter inlet.
[0027] In particular, the difference between use of an exhaust system comprising a catalyst
and a particulate filter which are incorporated inside a single housing (canister)
and the use of an exhaust system comprising a single filter with deposited thereon
both the oxidizing elements of the catalyst and metals which reduce the self-ignition
temperature consists in the fact that in the first type of exhaust system self-triggering
of regeneration occurs at about 600°C and the particulate filter has a low backpressure,
while in the second type of exhaust system self-triggering of regeneration occurs
at about 450°C, but the particulate filter has a high backpressure and there exists
both the risk of a reduced regeneration efficiency, owing to contact between the cesium
and the particulate, and the risk of drift in the regeneration efficiency, namely
an increase in the regeneration triggering temperature.
[0028] The appearance of second generation common-rail injection systems has resulted in
notable progress in the sector of particulate filter regeneration.
[0030] As is known, in fact, this type of injection system allows the execution, during
each engine cycle and inside each engine cylinder, of one or more of the following
injections, as shown in Figure 1, which details moreover the timing and the engine
angles at which injection is performed:
- a main injection MAIN performed in the vicinity of the combustion TDC;
- a pre-injection PRE prior to the main injection MAIN and performed sufficiently close
to the main injection MAIN to achieve continuity of combustion with the main injection
MAIN;
- a post-injection AFTER following the main injection MAIN and also performed sufficiently
close to the main injection MAIN to achieve continuity of combustion with the main
injection MAIN;
- a pre-injection PILOT prior to the pre-injection PRE, which is carried during the
compression step and is well in advance of the combustion TDC so much so that it does
not participate in combustion of the fuel injected during the pre-injection PRE; and
- a post-injection POST following the post-injection AFTER and performed with a notable
delay relative to the combustion TDC so as not to participate in combustion of the
fuel injected during the post-injection AFTER.
[0031] Each of the injections listed above produces a specific effect on operation of the
engine which allows a well-defined object to be achieved.
[0032] In particular:
- the injection PILOT causes an increase in the pressure inside the cylinder at the
end of the compression phase and this increase consequently produces a reduction in
the engine start-up time, a reduction in the noise and smokiness of the engine during
the transient warm-up phase of the engine and an increase in the torque output by
the engine at low speeds;
- the injection PRE causes a reduction in the ignition delay, namely the time which
lapses between injection of the fuel inside the main cylinder MAIN and the actual
start of combustion inside the cylinder and this reduction in the ignition delay consequently
causes a reduction in the combustion noise produced by the engine;
- the injection AFTER causes post-oxidation of the exhaust gases inside the cylinder
and this post-oxidation causes consequently a reduction in the quantity of particulate
generated during combustion; and
- the injection POST causes injection of a quantity of fuel during the exhaust phase
which, since actual combustion has already terminated, is not burnt and reaches the
exhaust unaltered, thus determining an increase in the hydrocarbons HC which are present
in the exhaust and which, in turn, activate the DeNOx catalyst, causing an increase
in the efficiency thereof. The exothermic oxidation reaction which occurs inside the
DeNOx catalyzer also causes raising of the temperature of the exhaust gases at the
inlet of the particulate filter which, as is known, is situated downstream of the
DeNOx catalyzer, allowing regeneration of the particulate filter.
[0033] It is also possible to divide the injection MAIN into two separate injections so
as to produce a reduction in the temperature peaks produced by combustion and, consequently,
a reduction in the quantity of nitrogen oxides NOx produced during combustion.
[0035] Owing to the extreme flexibility of the second generation common-rail injection systems,
in
European patent application 02017387.8 filed on 2.8.2002 by the Applicant and published on 5.2.2003 under number
EP-A-1, 281, 852, it was proposed achieving raising of the temperature of the exhaust gases necessary
for regeneration of the particulate filter by simply adjusting timing of one or more
of the injections with respect to the timing which they assume when regeneration of
the particulate filter is instead not performed.
[0036] In particular, a detailed study carried out by the Applicant has led to the definition,
for each operating point of the engine, of particular combinations and timings of
the multiple injections described above which allow self-triggering of regeneration
of the particulate filter.
[0037] In addition to this, the study carried out by the Applicant was able to verify how
the effect of these particular timings and combinations of the multiple injections
on regeneration of the particulate filter may be further improved by adjusting other
parameters of the engine and/or the injection system, such as the flowrate of the
intake air, the injection pressure and the quantity of exhaust gases which are recirculated.
[0038] In particular, broadly speaking the methods for regeneration of the particulate filter
highlighted by the Applicant envisage the following actions for raising the temperature
of the exhaust gases at the inlet of the particulate filter:
- performing three or four of the injections PILOT, PRE, MAIN and AFTER with a suitable
delay relative to the timings of the injections performed in conditions where there
is no regeneration of the particulate filter, said injections taking part in the combustion
process and allowing a delayed and stable combustion to be achieved, raising the temperatures
of the exhaust gases; and
- performing the post-injection POST so as to supply hydrocarbons HC to the DeNOx oxidizing
catalyzer situated upstream of the particulate filter and make use of the consequent
exothermic oxidation reaction thereof in order to raise thus further the temperature
of the exhaust gases at the outlet of the oxidizing catalyzer and therefore at the
inlet of the particulate filter.
[0039] The presence of a post-injection POST performed with a large delay with respect to
the combustion TDC (100°-180° after the TDC) is indispensable for correct operation
of the method for particulate filter regeneration proposed in the abovementioned patent
application
EP-A-1,281,852, but has drawbacks associated with the problem of dilution of the lubricating oil.
[0040] In fact, the considerable distance from the combustion TDC in terms of crank angle,
which is a characteristic of this type of injection, has the effect that the charging
conditions inside the cylinder (in particular the pressure and temperature values)
are unfavourable from the point of view of penetration of the jet of injected fuel.
Essentially, in these conditions, the aerodynamic resistance of the charge and the
heat exchanges between the latter and the liquid jet are not sufficient to prevent
part of the fuel injected with the injection POST from striking the film of lubricating
oil present on the cylinder liners. The droplets of fuel, following contact with the
film of lubricating oil, are enveloped inside the said film, in view of the perfect
miscibility between the two liquids. With each engine cycle, the veil of lubricating
oil contaminated with fuel is conveyed back into the oil sump by one of the resilient
rings mounted around the piston (so-called oil scraper rings).
[0041] The procedure described above is not the only way in which the fuel is able to come
into contact with the lubricating oil.
[0042] In fact, owing to the blow-by flow, part of the gases inside the cylinder containing
a high percentage of non-combusted hydrocarbons pass by the piston rings directly
into the oil sump. Obviously the level and the speed with which the two liquids interact
depends on the operating conditions of the engine and on the conditions in which the
vehicle is used.
[0043] The problems described above are aggravated by the fact that, in order to be able
to inject during the injection POST the quantities of fuel necessary for reaching
the temperature at which oxidation of the particulate is activated, it is required
to operate with maximum penetration of the fuel jet where the jet strikes the cylinder
walls; this inevitably results in interaction between the film of lubricating oil
and the fuel.
[0044] The exposure of the lubricating oil to the fuel results in dilution thereof, expressed
as a percentage by weight of fuel present inside the solution, and therefore an alteration
of the lubricating properties. In particular, this alteration results in a reduction
in the kinematic viscosity of the lubricating oil, which constitutes the main parameter
for assessing the quality of the lubricating oil.
[0045] From the literature on the subject it can be stated that even a reduction in the
viscosity in the region of 30% requires replacement of the lubricating oil, since
the latter is no longer able to perform its main functions (reduction of friction,
protection of mechanical parts against wear, heat disposal, etc.).
[0046] The problem of dilution of the lubricating oil described above is present during
the injection POST and therefore during regeneration of the particulate filter over
the whole operating range of the engine; however, it becomes even more critical at
engine points with low revolutions/loads. In fact at these engine points, the conditions
inside the cylinder are less favourable for the purposes of a reduction in penetration
of the fuel jet, and the quantities of fuel injected during the injection POST necessary
for reaching the temperature triggering oxidation of the particulate are higher.
[0047] Documents
EP-A-1 108 876,
EP-A-1 172 531 and
EP-A-1 160 435 disclose methods for controlling an internal combustion engine, envisaging the possibility
of performing multiple injections of fuel in the expansion or exhaust strokes so that
the injected fuel reaches in an unburned state an exhaust gas after-treatment devices.
[0048] The object of the present invention is that of providing a method for controlling
an internal combustion engine during regeneration of the particulate filter, which
is able to overcome the drawbacks described above.
[0049] The above object is achieved by the present invention in that it relates to a method
for controlling a diesel engine as claimed in claim 1.
[0050] For better understanding of the present invention, a preferred embodiment thereof
is now described purely by way of a non-limiting example with reference to the accompanying
drawings in which:
- Figure 1 shows a time, diagram of the multiple injections which can be performed with
a common-rail injection system; and
- Figure 2 shows the temporal division of the post-injection POST according to a preferred
embodiment of the present invention.
[0051] The idea underlying the present invention is based on the realization that the abovementioned
problem of dilution of the lubricating oil due to mixing with the fuel injected inside
the cylinder during the injection POST may be eliminated, or at least greatly reduced,
by acting on the way in which the jet of fuel is injected inside the cylinder, with
the aim of modifying the penetration of the said jet and ensuring that the lubricating
oil is exposed only minimally to the fuel.
[0052] In this connection, there are various parameters which help determine the method
of penetration of the fuel in the liquid phase inside the cylinder following an injection.
Of these parameters, the main ones are as follows:
- parameters associated with the processes which occur during vaporization of the fuel
droplets, including mixing with air, exchange of energy between the gaseous phase
and liquid phase, etc.;
- parameters associated with the engine settings, including the quantity of fuel injected
during each injection, the injection pressure, the duration of injection, etc.;
- parameters associated with the charging conditions inside the cylinder, including
the temperature and the pressure of the gases; and
- parameters dependent upon the engine characteristics, including the size of the injector
holes, the type of electric command imparted to the injector, etc.
[0053] Of the parameters listed above, the present invention envisages modulating the quantity
of fuel injected during the injection POST, in order to control penetration of the
fuel jet inside the cylinder.
[0054] In detail, according to a feature of the invention, the injection POST is divided
into a suitable number of fractions so that the individual fractions possess a quantity
of movement which is less than the quantity of movement possessed individually by
the injection POST of the known type. In this way the capacity of the fuel to penetrate
inside the cylinder and consequently the exposure of the lubricating liquid to the
said fuel is reduced. In other words, by dividing the injection POST into several
fractions it is possible to adapt the quantity of injected fuel to the charging conditions
inside the cylinder and therefore to the aerodynamic resistance offered by the gases
to the fuel jet.
[0055] In particular, in a preferred embodiment of the present invention, the number of
injections into which the injection POST is divided is at the most three and is determined
on the basis of the engine point.
[0056] Figure 2 shows a time diagram relating to the method of multiple injection of fuel
performed in accordance with a preferred embodiment of the method for controlling
an engine according to the present invention.
[0057] In particular, in the first part of the time diagram, it is possible to identify
the injections PILOT, PRE, MAIN and AFTER described above with reference to the state
of the art. According to the invention, in the second part of the time diagram, instead
of a single injection POST, three separate fractions are present, indicated by POST1,
POST2 and POST3, respectively. In a manner similar to that of the state of the art,
the first fraction POST1 is separated from the injection AFTER by a time interval
which is greater than or equal to 89 µs so as to intervene once combustion inside
the cylinder has been completed.
[0058] The quantities of fuel to be injected during the various fractions POST1, POST2 and
POST3 is determined from the total quantity of fuel QPOST to be injected during the
injection POST, calculated on the basis of the engine point.
[0059] In detail, firstly the quantity of fuel to be injected during the last two fractions
POST2 and POST3, indicated by QPOST2 and QPOST3, respectively, is determined in percentage
terms with respect to the total quantity to be injected QPOST and then the quantity
of fuel to be injected during the first fraction POST1, indicated by QPOST1, is calculated,
as the difference between the total quantity QPOST and the sum of the quantities QPOST2
and QPOST3.
[0060] Since electric injectors are unable to inject a quantity of fuel less than a predefined
minimum threshold, in the case where one of the quantities of fuel to be injected
QPOST2 and QPOST3 is less than this predefined minimum threshold, the two fractions
POST2 and POST3 are combined.
[0061] Moreover, if also the sum of the two quantities QPOST2 and QPOST3 is less than the
predefined minimum threshold, then all three fractions POST1, POST2 and POST3 are
combined, thus resulting in return to the solution with single injection POST.
[0062] As regards timing of the various fractions, firstly the starting point of the first
fraction POST1 is fixed (indicated in the figure by SOIPost1) so, that it occurs at
an engine angle such as not to participate in combustion inside the cylinder. Typically
the time interval between the end of the injection AFTER and the start of the first
fraction POST1 is greater than or equal to 89 µs. Subsequently, depending on the engine
point, the relative positions of the last two fractions POST2 and POST3 are determined
by means of choice of a suitable dwell time between the first and the second fraction,
DTPost2, and between the second and third fraction, DTPost3 (the term "dwell time"
indicates the distance between the end of the electric command for an injection and
the start of the electric command for the next injection inside the same cylinder).
[0063] From an examination of the characteristics of the method for controlling an internal
combustion engine during regeneration of the particulate filter performed in accordance
with the present invention the advantages which can be obtained therewith are obvious.
[0064] In particular, the division of the injection POST into several fractions allows,
for the same quantity of fuel injected and charging conditions inside the cylinder,
a reduction in dilution of the lubricating oil due to regeneration of the particulate
filter and therefore preservation of the lubricating properties and an increase in
the duration of the said lubricating oil.
[0065] The abovementioned advantages are valid over the whole operating range of the engine,
but assume greater importance during operation at low speeds/loads. In this condition,
in fact, the quantity of fuel injected during the injection POST is maximum, owing
to the high difference between the temperature of the exhaust gases during normal
operation and the target temperature for regeneration, and the charging conditions
inside the cylinder are most unfavourable from the point of view of resistance to
penetration of the fuel jet.
[0066] Finally, it is obvious that modifications and variations may be made to the method
for controlling an internal combustion engine during regeneration of the particulate
filter described and illustrated here, without thereby departing from the scope of
protection of the present invention, as defined in the accompanying claims.
[0067] In particular, it is clear that it is possible to vary the number of fractions into
which the injection POST is divided, their relative position with respect to the combustion
TDC and the quantity of fuel injected during the individual fractions.
1. Method for controlling a diesel engine provided with a common-rail injection system,
a DeNOx oxidizing catalyser and a particulate filter arranged downstream of said DeNOx
oxidizing catalyser, comprising the steps of:
- performing at least one main fuel injection (PRE, MAIN) into a cylinder of said
engine, the injected fuel being intended to take part in a combustion inside said
cylinder, and
- performing a fuel post-injection (POST) in order to inject a total quantity of fuel
(QPOST) inside said cylinder, said fuel post-injection being so separated from said
main fuel injection (PRE, MAIN) that the fuel injected during said fuel post-injection
does not take part in said combustion and reaches said DeNOx oxidizing catalyser at
least in part in an unburned state in order to cause an exothermic reaction in said
DeNOx oxidizing catalyser;
said method further comprising the step of performing an auxiliary fuel injection
(AFTER) after and so close to said main fuel injection (PRE, MAIN) as to combust inside
said cylinder,
characterized by comprising the step of dividing said fuel post-injection (POST) into a plurality
of separate fuel post-injections (POST1, POST2, POST3),
and in that the timing and quantity of said auxiliary fuel injection (AFTER) is such
as to cause a first increase in the temperature of the exhaust gases reaching said
DeNOx oxidizing catalyser, and the quantity and timing of said fuel post-injection
(POST) is such as to cause a second increase in the temperature of said exhaust gases,
the combination of said first and second increases determining a target temperature
of said exhaust gases at the inlet of said particulate filter, such as to cause regeneration
thereof.
2. Method according to claim 1, in which said step of dividing up said fuel post-injection
comprises the step of calculating a number of fuel post-injections on the basis of
an operating point of said engine.
3. Method according to any one of the preceding claims, in which said plurality of fuel
post-injections comprises at the most three fuel post-injections (POST1, POST2, POST3).
4. Method according to any one of the preceding claims, in which said step of dividing
up said fuel post-injection comprises the step of dividing up said total quantity
of fuel (QPOST) into said plurality of fuel post-injections (POST1, POST2, POST3).
5. Method according to any one of the preceding claims, in which said plurality of fuel
post-injections comprises an initial fuel injection (POST1), an intermediate fuel
injection (POST2) and a final fuel injection (POST3) and in which said step of dividing
up said fuel post-injection comprises the steps of:
- calculating an intermediate quantity of fuel (QPOST2) to be injected during said
intermediate fuel injection (POST2) and a final quantity of fuel (QPOST3) to be injected
during said final fuel injection (POST3), as predefined percentages of said total
quantity of fuel (QPOST); and
- calculating an initial quantity of fuel (QPOST1) to be injected during said initial
fuel injection (POST1), as the difference between said total quantity of fuel (QPOST)
and said intermediate and final quantities of fuel (QPOST2, QPOST3).
6. Method according to claim 5, also comprising the steps of comparing said intermediate
and final quantities of fuel (QPOST2, QPOST3) with a predefined minimum threshold
and activating said initial fuel injection (POST1), intermediate fuel injection (POST2)
and final fuel injection (POST3) if both said intermediate and final quantities of
fuel are greater than said predefined minimum threshold.
7. Method according to claim 6, comprising the steps of calculating a combined quantity
of fuel equal to the sum of said intermediate and final quantities of fuel (QPOST2,
QPOST3) if at least one of said intermediate and final quantities of fuel is less
than said predefined minimum threshold.
8. Method according to claim 7, also comprising the step of comparing said combined quantity
of fuel with said predefined minimum threshold and activating said initial fuel injection
(POST1) with said initial quantity of fuel (QPOST1) and a single successive fuel injection
with said combined quantity of fuel if said combined quantity of fuel is greater than
said predefined minimum threshold.
9. Method according to claim 8, comprising the steps of activating a single fuel injection
with said total quantity of fuel (QPOST) if said combined quantity of fuel is less
than said predefined minimum threshold.
10. Method according to claim 6, in which said step of performing a fuel post-injection
(POST) comprises the steps of:
- determining an initial instant (SOIPost1) of said initial fuel injection (POST1)
on the basis of an operating point of said engine; and
- determining time separation intervals (DTPOST2, DTPOST3) between said initial fuel
injection (POST1) and said intermediate fuel injection (POST2) and between said intermediate
fuel injection (POST2) and said final fuel injection (POST3), on the basis of said
operating point.
1. Verfahren zum Steuern eines Dieselaggregates, bereitgestellt mit einem Common-Rail-Einspritzsystem,
einem DeNOx-Oxidationskatalysator und einem Partikelfilter, angeordnet flussabwärtsliegend
des DeNOx-Oxidationskatalysators, umfassend die Schritte:
- Durchführung von zumindest einer Hauptbrennstoffeinspritzung (PRE, MAIN) in einen
Zylinder des Aggregates, wobei der eingespritzte Brennstoff beabsichtigt ist an einer
Verbrennung innerhalb des Zylinders teilzunehmen, und
- Durchführung einer Brennstoffnacheinspritzung (POST) um eine Gesamtmenge an Brennstoff
(QPOST) ins Innere des Zylinders einzuspritzen, wobei die Brennstoffnacheinspritzung
derart von der Hauptbrennstoffeinspritzung (PRE, MAIN) getrennt ist, dass der Brennstoff,
eingespritzt während der Brennstoffeinspritzung, nicht an der Verbrennung teilnimmt
und den DeNOx-Oxidationskatalysator zumindest teilweise in einem unverbrannten Zustand
erreicht um eine exotherme Reaktion in dem DeNOx-Oxidationskatalysator zu veranlassen;
wobei das Verfahren des Weiteren den Schritt umfasst des Durchführens einer Hilfsbrennstoffeinspritzung
(AFTER) nach oder anschließend und so nahe zu der Hauptbrennstoffeinspritzung (PRE,
MAIN) als das eine Verbrennung innerhalb des Zylinders stattfindet,
dadurch gekennzeichnet, dass das Verfahren den Schritt umfasst des Aufteilens der Brennstoffnacheinspritzung (POST)
in eine Vielzahl von separaten Brennstoffnacheinspritzungen (POST1, POST2, POST3),
und dadurch, dass die Zeitgebung und Menge an Hilfsbrennstoffeinspritzung (AFTER)
derart ist, dass ein erster Temperaturanstieg der Abgase veranlasst ist/wird, die
den DeNOx-Oxidationskatalysator erreichen, und die Menge und Zeitgebung der Brennstoffnacheinspritzung
(POST) derart ist, dass ein zweiter Temperaturanstieg der Abgase veranlasst ist/wird,
wobei die Kombination der ersten und zweiten Anstiege eine Zieltemperatur der Abgase
am Einlass des Partikelfilters derart bestimmt, dass eine Regeneration desselben veranlasst
ist/wird.
2. Verfahren nach Anspruch 1, bei welchem der Schritt des Aufteilens der Brennstoffnacheinspritzung
den Schritt umfasst des Berechnens einer Anzahl von Brennstoffnacheinspritzungen auf
der Grundlage eines Betriebspunktes des Aggregates oder Motors.
3. Verfahren nach einem der vorangegangen Ansprüche, bei welchen die Vielzahl an Brennstoffnacheinspritzungen
höchstens drei Brennstoffnacheinspritzungen (POST1, POST2, POST3) umfasst.
4. Verfahren nach einem der vorangegangen Ansprüche, bei welchem der Schritt des Aufteilens
der Brennstoffnacheinspritzungen den Schritt umfasst des Aufteilens der Gesamtmenge
an Brennstoff (QPOST) in die Vielzahl von Brennstoffnacheinspritzungen (POST1, POST2,
POST3).
5. Verfahren nach einem der vorangegangen Ansprüche, bei welchem die Vielzahl an Brennstoffnacheinspritzungen
eine anfängliche Brennstoffeinspritzung (POST1), eine mittlere Brennstoffeinspritzung
(POST2) und eine Endbrennstoffeinspritzung (POST3) umfasst, und bei welcher der Schritt
des Aufteilens der Brennstoffnacheinspritzung die Schritte umfasst:
- Berechnen einer mittleren Menge an Brennstoff (QPOST2), die einzuspritzen ist während
der mittleren Brennstoffeinspritzung (POST2), und einer Endmenge an Brennstoff (QPOST3),
einzuspritzen während der Endbrennstoffeinspritzung (POST3), und zwar als vorbestimmte
prozentuale Anteile der Gesamtmenge an Brennstoff (QPOST);
- Berechnen einer anfänglichen Menge an Brennstoff (QPOST1), einzuspritzen während
der anfänglichen Brennstoffeinspritzung (POST1), als die Differenz zwischen der Gesamtmenge
an Brennstoff (QPOST) und den mittleren und Endmengen an Brennstoff (QPOST2, QPOST3).
6. Verfahren nach Anspruch 5, ferner umfassend die Schritte des Vergleichens der mittleren
und Endmengen an Brennstoff (QPOST2, QPOST3) mit einem vorbestimmten Minimalschwellenwert
und des Aktivierens der anfänglichen Brennstoffeinspritzung (POST1), der mittleren
Brennstoffeinspritzung (POST2) und der Endbrennstoffeinspritzung (POST3), wenn sowohl
die mittlere als auch die Endmengen an Brennstoff größer sind als der vorbestimmte
Minimalschwellenwert.
7. Verfahren nach Anspruch 6, umfassen die Schritte des Berechnens einer kombinierten
Menge an Brennstoff gleich zu der Summe der mittleren und Endmengen an Brennstoff
(QPOST2, QPOST3), wenn zumindest eine der mittleren und Engmengen an Brennstoff geringer
ist als der vorbestimmte Minimalschwellenwert.
8. Verfahren nach Anspruch 7, ferner umfassend den Schritt des Vergleichens der kombinierten
Menge an Brennstoff mit dem vorbestimmten Minimalschwellenwert und des Aktivierens
der anfänglichen Brennstoffeinspritzung (POST1) mit der anfänglichen Menge an Brennstoff
(QPOST1) und einer einzelnen nachfolgenden Brennstoff einspritzung mit der kombinierten
Menge an Brennstoff, wenn die kombinierte Menge an Brennstoff größer ist als der vorbestimmte
Minimalschwellenwert.
9. Verfahren nach Anspruch 8, umfassend die Schritte des Aktivierens einer einzelnen
Brennstoffeinspritzung mit der Gesamtmenge an Brennstoff (QPOST), wenn die kombinierte
Menge an Brennstoff geringer ist als der vorbestimmte Minimalschwellenwert.
10. Verfahren nach Anspruch 6, bei welchem der Schritt des Durchführens einer Brennstoffnacheinspritzung
(POST) die Schritte umfasst von :
- bestimmen eines anfänglichen Momentes (SOIPOST1) der anfänglichen Brennstoff einspritzung
(POST1) auf der Grundlage eines Betriebspunktes des Aggregates oder Motors;
- bestimmen von Zeittrennintervallen (DTPOST2, DTPOST3) zwischen der anfänglichen
Brennstoffeinspritzung (POST1) und der mittleren Brennstoffeinspritzung (POST2) und
zwischen der mittleren Brennstoffeinspritzung (POST2) und der Endbrennstoffeinspritzung
(POST3), und zwar auf der Grundlage des Betriebspunktes.
1. Procédé de commande d'un moteur diesel pourvu d'un système d'injection à rampe commune,
d'un catalyseur d'oxydation DeNOx et d'un filtre à particules agencé en aval dudit
catalyseur d'oxydation DeNOx, comprenant les étapes :
- d'exécution d'au moins une injection de carburant principale (PRE, MAIN) dans un
cylindre dudit moteur, le carburant injecté étant destiné à prendre part à une combustion
à l'intérieur dudit cylindre, et
- d'exécution d'une post-injection de carburant (POST) afin d'injecter une quantité
de carburant totale (QPOST) à l'intérieur dudit cylindre, ladite post-injection de
carburant étant séparée de ladite injection de carburant principale (PRE, MAIN) de
sorte que le carburant injecté pendant ladite post-injection de carburant ne prend
pas part à ladite combustion et atteint ledit catalyseur d'oxydation DeNOx au moins
en partie dans un état non brûlé afin de provoquer une réaction exothermique dans
ledit catalyseur d'oxydation DeNOx ;
ledit procédé comprenant en outre l'étape d'exécution d'une injection de carburant
auxiliaire (AFTER) après et si proche de ladite injection de carburant principale
(PRE, MAIN) qu'il brûle à l'intérieur dudit cylindre,
caractérisé en ce qu'il comprend l'étape de division de ladite post-injection de carburant (POST) en une
pluralité de post-injections de carburant (POST1, POST2, POST3) séparées,
et en ce que la synchronisation et la quantité de ladite injection de carburant auxiliaire (AFTER)
sont telles qu'elles provoquent une première augmentation de la température des gaz
d'échappement atteignant ledit catalyseur d'oxydation DeNOx, et la quantité et la
synchronisation de ladite post-injection de carburant (POST) sont telles qu'elles
provoquent une deuxième augmentation de la température desdits gaz d'échappement,
la combinaison desdites première et deuxième augmentations déterminant une température
cible desdits gaz d'échappement à l'entrée dudit filtre à particules, telle qu'elle
provoque la régénération de ceux-ci.
2. Procédé selon la revendication 1, dans lequel ladite étape de division de ladite post-injection
de carburant comprend l'étape de calcul d'un nombre de post-injections de carburant
sur la base d'un point de fonctionnement dudit moteur.
3. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
pluralité de post-injections de carburant comprend au plus trois post-injections de
carburant (POST1, POST2, POST3).
4. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
étape de division de ladite post-injection de carburant comprend l'étape de division
de ladite quantité de carburant totale (QPOST) en ladite pluralité de post-injections
de carburant (POST1, POST2, POST3).
5. Procédé selon l'une quelconque des revendications précédentes, dans lequel ladite
pluralité de post-injections de carburant comprend une injection de carburant initiale
(POST1), une injection de carburant intermédiaire (POST2) et une injection de carburant
finale (POST3), et dans lequel ladite étape de division de ladite post-injection de
carburant comprend les étapes :
- de calcul d'une quantité de carburant intermédiaire (QPOST2) à injecter pendant
ladite injection de carburant intermédiaire (POST2) et d'une quantité de carburant
finale (QPOST3) à injecter pendant ladite injection de carburant finale (POST3), en
tant que pourcentages prédéfinis de ladite quantité de carburant totale (QPOST) ;
et
- de calcul d'une quantité de carburant initiale (QPOST1) à injecter pendant ladite
injection de carburant initiale (POST1), en tant que différence entre ladite quantité
de carburant totale (QPOST) et lesdites quantités de carburant intermédiaire et finale
(QPOST2, QPOST3).
6. Procédé selon la revendication 5, comprenant également les étapes de comparaison desdites
quantités de carburant intermédiaire et finale (QPOST2, QPOST3) avec un seuil minimum
prédéfini et d'activation desdites injection de carburant initiale (POST1), injection
de carburant intermédiaire (POST2) et injection de carburant finale (POST3) si lesdites
quantités de carburant intermédiaire et finale sont toutes deux supérieures au dit
seuil minimum prédéfini.
7. Procédé selon la revendication 6, comprenant les étapes de calcul d'une quantité de
carburant combinée égale à la somme desdites quantités de carburant intermédiaire
et finale (QPOST2, QPOST3) si au moins l'une desdites quantités de carburant intermédiaire
et finale est inférieure au dit seuil minimum prédéfini.
8. Procédé selon la revendication 7, comprenant également l'étape de comparaison de ladite
quantité de carburant combinée avec ledit seuil minimum prédéfini et d'activation
de ladite injection de carburant initiale (POST1) avec ladite quantité de carburant
initiale (QPOST1) et d'une injection de carburant successive unique avec ladite quantité
de carburant combinée si ladite quantité de carburant combinée est supérieure au dit
seuil minimum prédéfini.
9. Procédé selon la revendication 8, comprenant les étapes d'activation d'une injection
de carburant unique avec ladite quantité de carburant totale (QPOST) si ladite quantité
de carburant combinée est inférieure au dit seuil minimum prédéfini.
10. Procédé selon la revendication 6, dans lequel ladite étape d'exécution d'une post-injection
de carburant (POST) comprend les étapes :
- de détermination d'un instant initial (SOIPost1) de ladite injection de carburant
initiale (POST1) sur la base d'un point de fonctionnement dudit moteur ; et
- de détermination d'intervalles de séparation temporelle (DTPOST2, DTPOST3) entre
ladite injection de carburant initiale (POST1) et ladite injection de carburant intermédiaire
(POST2) et entre ladite injection de carburant intermédiaire (POST2) et ladite injection
de carburant finale (POST3), sur la base dudit point de fonctionnement.